The present invention relates to a process for treating brass. More particularly, the present invention is directed to a process of removing lead from the surface of brass fixtures.
Brass is an alloy composed principally of copper, tin zinc and lead. The amount of lead added to brass affects its strength, workability and machinability of the final alloy. Brass has been widely used for plumbing fittings, waterworks valves and fittings, bronze alloys and a host of other applications. Perhaps the most widespread application of brass is its use in the manufacture of faucets, valves, fittings, water meters, and related products intended for use in delivering potable water to and within commercial or residential sites. For such uses, the amount of lead that is required to affect the desired strength machinability of the brass causes concerns with the leachability of the lead into the environment where such faucets, valves, fittings and related products are used.
Lead exhibits a relatively low solubility in solid solution in brass alloys due to the atomic size of lead atoms which is larger than copper or zinc. The low solubility of lead in brass alloys causes the lead to precipitate in lead-rich regions dispersed throughout brass alloys. The tendency toward precipitation is particularly notable near the surface of brass articles. In addition to improving the machinability of brass adjacent to the surface, the precipitation of lead near the surface increases the tendency of lead present on the surface to leach into water.
Recent standards have significantly limited the acceptable amount of lead that can be leached from brass faucets, valves, fittings and related products. One such example is the Safe Drinking Water Act, amended in 1988, to limit lead in solders and fluxes to 0.2 percent and to limit lead in public water supply pipes and fittings to 8 percent.
Similarly, efforts have been underway to limit the amount of lead found in food or water. California, for example, has promulgated regulations limiting lead exposure of an individual to less than 0.5 micrograms per day. On the Federal level, the EPA, in 1991, restructured the standard of lead in drinking water from 50 parts per billion to 15 parts per billion.
While the amount of lead that can be leached from brass plumbing components is generally low, it is nonetheless possible that the amount of lead that can be leached from such components may exceed current or planned standards. It has been proposed that current standards be made even more stringent so that lead is omitted totally from brass alloys or that brass articles be treated so that minimum quantities of lead may be leached from such articles.
The present disclosure provides a simple, relatively efficient process for treating brass which removes leachable lead therefrom.
An illustrative disclosure provides a method of treating brass articles to reduce leachable lead therein. The method comprises the steps of, first contacting a brass article with a primary treatment solution to reduce leachable lead therein. The primary treatment solution comprises an aqueous caustic solution containing a chelating agent. The next step is contacting the brass article with a post-treatment solution after being contacted with the primary treatment solution. The post-treatment solution comprises an aqueous solution containing an azole.
In the above and other illustrative embodiments, the method of treating brass articles may also provide: the chelating agent being selected from the group consisting of phosphonic acids, aminopolycarboxlic acids and mixtures thereof; the chelating agent being selected from the group consisting of ethylenediaminetetraacetic acid, N-hydroxyethylethylene-diaminetriacetic acid, diethylenetriaminepentaacetic acid and mixtures thereof; the caustic solution including a caustic component selected from the group consisting of an alkali metal hydroxide, an alkali metal carbonate, an alkali metal phosphate and mixtures thereof; the brass article being sonicated during contact with the primary treatment solution; the brass article being contacted with a pretreatment solution prior to being contacted with the primary treatment solution, said pretreatment solution comprising an aqueous solution containing a sodium persulfate; the brass article being sonicated during contact with the pretreatment solution; the post-treatment solution being at a temperature of about 120 degrees Fahrenheit; the azole being selected from a group consisting of mercaptobezothiazole, benzotriazoles, and tolytriazole.
Another illustrative embodiment of the present invention also provides a method of treating brass articles to reduce leachable lead therein. This embodiment comprises the step of contacting a brass article with a treatment solution comprising an aqueous solution containing an azole.
In the above and other illustrative embodiments, the method of treating brass articles may also provide: the treatment solution being at a temperature of about 120 degrees Fahrenheit; the azole being selected from a group consisting of mercaptobezothiazole, benzotriazoles, and tolytriazole; the treatment being followed by a 70 degree Fahrenheit water rinse; the 70 degree Fahrenheit water rinse being followed by a 150 degree Fahrenheit ultrasonic water rinse; and the 150 degree Fahrenheit ultrasonic water rinse being followed by an azole rinse at 120 degrees Fahrenheit.
Additionally, in the above and other embodiments, the method of treating brass articles may provide: subsequent to contacting a brass article with a treatment solution comprising an aqueous solution containing the azole, the brass article being contacted with water; the water being at a temperature of about 80 to about 140 degrees Fahrenheit; contacting the brass article again with water having a temperature of about 80 to about 140 degrees Fahrenheit; the water being reverse osmosis water; contacting the brass article with an about 0.5 to about 5 percent benzotriazole solution; the about 0.5 to about 5 percent benzotriazole solution being at a temperature of about 80 to about 140 degrees Fahrenheit; contacting the brass article with the about 0.5 to about 5 percent benzotriazole solution for about 3 to about 15 minutes; contacting the brass article with the about 0.5 to about 5 percent benzotriazole solution subsequent to a water rinse; contacting the brass article again by water subsequent to contacting the brass article with the about 0.5 to about 5 percent benzotriazole solution.
Additional features and advantages of the method of treating brass articles will become apparent to those skilled in the art upon consideration of the following detailed description of the illustrated embodiment exemplifying the best mode of carrying out the method of treating brass articles as presently perceived.